1. Field of the Invention
The present invention relates to a digital cable broadcast receiver, and more particularly, to a digital cable broadcast receiver and a method for processing a caption thereof that can process a caption of a various types and standards for use in a digital cable broadcast, in an adaptive manner.
2. Discussion of the Related Art
A ground wave broadcast standard for an analog broadcast in USA (United States of America) is an NTSC (national television system committee) standard. The NTSC standard is characterized in transmitting a closed caption such as English, Spanish, using a 21st line of a VBI (vertical blanking interval) of a broadcast signal. A standard related to the transmission of the closed caption is an EIA (electronic industry association) standard 608. Services provided through a 21st line of the VBI under the EIA 608 standard are as follows: CC1 (primary synchronous caption service), CC2 (special asynchronous caption service), CC3 (secondary synchronous caption service), CC4 (special asynchronous caption service), Text1 (first letter information service), Text2 (second letter information service), Text3 (third letter information service), Text4 (fourth letter information service).
In USA, a user has to select, in person, one among the above-mentioned services. Further, since there is no information as to which service is provided among the above-mentioned eight services while a broadcast program is displayed, there has been a difficulty that a user should check, case by case, the services so as to check a service under execution.
A ground wave broadcast standard for a digital broadcast in USA is an ATSC (advanced television system committee) standard. Further, an EIA 708, which is a standard on a digital TV closed caption (DTVCC), is established. The DTVCC will be described with reference to the accompanying drawings. FIG. 1 illustrates the general bit stream provided to a digital TV. As shown in FIG. 1, the bit stream includes: audio data, video data, control data (i.e., supplementary information). Data that corresponds to the DTVCC is included in user_data bits of the video data and transmitted under an MPEG-2 (Moving Picture Experts Group-2) video standard and the ATSC standard (A53). At this point, according to the above standards, the DTVCC data can be transmitted up to as much as 128 bytes at its maximum for each user_data region and the total transmission amount cannot exceed 9600 bps (bit per second). Compared with an analog closed caption based on the EIA 608, where the total transmission amount cannot exceed 960 bps, the DTVCC based on the EIA 708 has realized ten times greater bandwidth in its data transmission. The DTVCC based on the EIA 708 can provide sixty-three caption services in total with consideration of the extended bandwidth. In case of the sixty-three digital caption services, there is a difficulty that a user should change settings to find out a desired caption service as was done in the above-described analog closed caption. Due to such reason, in case of providing a DTVCC according to the ATSC standard, a broadcast station must include information called a caption_service_descriptor within an EIT (event information table) or a PMT (program map table) in a PSIP (program and system information protocol). The EIT and the caption_service_descriptor allow a DTV receiver to know what kind of the DTVCC is included in a relevant program.
The cable broadcast is a little different from the ground wave broadcast depending on regions, or service companies, or broadcast equipments. In particular, the cable broadcast is the same as the ground wave analog broadcast in that transmission is performed on the basis of a letter value and a command set prescribed by the EIA 608 in operating a closed caption. However, the cable broadcast is different from the ground wave broadcast in transmitting the closed caption using other interval of the VBI except a 21st line of the VBI. That is, some broadcast station transmits a caption using a sixth line of the VBI while other broadcast station transmits a caption using a tenth line. In the meantime, as an analog cable broadcast is switched into a digital cable broadcast, a closed caption standard regarding the digital broadcast has been established independently. The basic object of standards tilted SCTE (society of cable television engineers) 20 and DVS (digital video surveillance) 157 is to convert an analog closed caption for use in the analog cable broadcast into user_data within a video data region for use in a digital TV. Those standards do not include content regarding a DTVCC of the EIA 708standard but only prescribe content regarding the analog closed caption as is done in the existing standards.
The ATSC standard regarding the DTVCC does not consider the closed caption under the SCTE 20 or the DVS 157 which are caption transmission standards for use in the cable broadcast. Since a cable broadcast service company has provided a cable set top box appropriate for the company's broadcast to each user, there was little problem in a digital-cable-broadcast generation before an open-cable generation. However, under a new digital broadcast environment such as an open cable and a Cable Ready, there occur problems regarding the standards. That is, under the open cable and the Cable Ready environments whose object is to connect an apparatus generally available in the market, not a specific cable broadcast receiver provided by a specific cable broadcast company, to a cable, a method for transmitting/receiving a caption emerges as a very complicated problem.
An open cable broadcast signal under regulations of a FCC (federal communications commission) must include a DTVCC and an analog CC (closed caption) prescribed by the EIA 708. Further, the open cable broadcast signal should include user_data of other type prescribed by the SCTE 20 or the DVS 157 and may include a relevant caption at a S-Video, a Composite, a 480i, and a VBI line of the Component output. Therefore, the cable broadcast receiver should know what kind of caption data is included in a digital cable broadcast being received. However, it is difficult for the cable broadcast receiver to judge a kind of caption data being received in view of characteristics of caption data. Accordingly, a user should check in person the caption data through a key or a menu on a remote control. Also, a user should experimentally select and check what kind of caption data is decoded.